Make no mistake -- the well IS running dry. This "well" contains the primary energy sources, oil, natural gas, coal and uranium, that now power our world. They are limited. Oil will run out first, then the others. Twenty years, fifty years, experts disagree only on the time frame, something else is needed, energy sources which will take over entirely by the year 2100.

There ARE “renewable” energy sources. These will NEVER run out. Two thousand years from now they will be providing the energy needs of the 40th century. There are several of these. Which one (or possibly two or three) will prevail? This is what it looks like to me, assuming continuing engineering improvements, but no great technological inventions:

1. Biofuels. No, not made from corn, but from algae and weed-based stock. The energy content of a biofuel is comparable to that of gasoline, one of the most flexible energy sources we know. Biofuels, supplemented by hybrid battery technologies, will run our autos and light trucks. A less costly source, however, will be used for electricity, heating, cooling and lighting our homes and businesses, running our factories, etc.

2. Solar power can potentially provide all the energy the world needs. It's not an energy source for your car; far too little power is generated by a solar panel on a car roof, even at 100% efficiency. There will be solar roof panels on many buildings, solar "farms" in the Nevada desert, and an improved electric grid to distribute the energy. By 2100 AD, this will be the world's primary energy source.

3. Wind power, currently growing 25% yearly, is already significant. The wind blows for free. The potential energy available is about ten times current world energy consumption. While many engineering problems remain to be solved, mostly involving power storage and the electric grid, it could be an ultimate winner.. But wind farms take up land, and most locations have too little wind to be productive. Look for this energy source to increase over the next twenty to fifty years, but not dominate in the long term.

4. Geothermal power plants alone could suffice our planet's needs for well over 1,000 years. Each plant, however, is a unique engineering challenge, and the economics are not clear. I look for them to be a minor part of the mix for a few decades, but not a significant long term solution.

5. Wave and tidal energies from the ocean might be harnessed. But this source does not seem to be large enough to be a winner, although there are several apparently successful pilot plants.

6. A very long shot -- nuclear plants built on the fusion principle. Research on these has been ongoing for 50 years. The "solution" is always 40 years away. I don't see a breakthrough for this technology. If one happens, this energy source will be the big winner. In the short term, through 2050, conventional nuclear plants will play a larger part than today, but solar is going to win out.

7. What about hydrogen for auto fuel? Hydrogen is a fuel -- not a fuel source. Pound for pound, gasoline is three times the power. A car with a 20 gallon gas tank would need a 60 gallon tank if it were to be converted to liquid hydrogen, and a 120 gallon tank if pressurized hydrogen were substituted. Basic physics "kills" the idea except for specialized applications.

8. What about all-electric cars? Again, physics intervenes. A 20 gallon tank carries about 120 pounds of fuel. To get the same range with present-day battery technology, you'd need 3,600 pounds of battery -- at ten times the storage space of your present tank. Yes, this is likely to improve over time. Keep watching. Several brands of limited range all-electric autos are planned to be announced in the next three years.

In the meantime, invest in the future. Buy the new energy efficient light bulbs. Consider a hybrid car. Keep studying the issues. And for heaven's sake, don't fall for the "drill, baby, drill" yahoos! They offer, at best, oil-based stopgap solutions, and do nothing to ensure our grandkids' future!